1. Field of the Invention
The present invention relates to an automatic defect inspection apparatus for a color filter and, more particularly, to an automatic defect inspection apparatus for a color filter, which is suitably used in automatic defect detection/inspection of a color filter which is, in turn, used in, e.g., a liquid crystal display device and has a spatially periodical repetitive structure of red, green, and blue.
2. Related Background Art
In conventional defect inspection of color filters used in, e.g., a liquid crystal display device, an inspection person normally visually inspects all the filters. Since this defect inspection method depends on sensory organs of man, the defect inspection result varies depending on the physical conditions and individual differences of the inspection persons, and it is difficult to attain stable defect inspection.
Also, various methods of automatically detecting defects using machines independently of the sensory organs of man have been proposed. However, these methods are still in the process of experimentation, and are not put into practical applications.
Of automatic defect inspection apparatuses which have been proposed, an automatic defect inspection apparatus which uses a video camera comprising a line sensor such as a CCD as detection means for detecting light from a color filter is known. In this defect inspection apparatus, since too small an area corresponding to one pixel of the line sensor is used as one measurement unit, a large volume of measurement data must be subjected to arithmetic processing, and a special-purpose arithmetic device capable of performing high-speed arithmetic processing is required, resulting in a very expensive apparatus.
Furthermore, since all the conventionally proposed automatic defect inspection apparatuses for color filters have a structure for detecting patterns of defects, they have insufficient detection performance for defects with unclear edges such as unevenness, a shadowy portion, and the like which are not so serious but are present in a wide area or range.
Note that the types of defects of a color filter include a projection, white hole, white shadowy portion, color mixing, unevenness, and the like. The projection is a portion of a color filter, which projects on the color filter, and the white hole is a defect which appears white in a narrow area as if a hole were formed in the color filter. Also, the white shadowy portion is a defect which appears to be shadowy white in a relatively wide area as if the colors of the color filter were lightened, and the color mixing indicates a portion where red, green, and blue color filters are locally mixed. Furthermore, the unevenness indicates a portion which appears to be so-called "unevenness" when the color filter is observed, and is a defect which has a lower contrast and a wider area than those of the "hole". Note that other defects of the color filter include a "black hole" which is a defect observed black due to foreign matter mixed in the filter, an "unusual black line" which indicates a portion of a black line suffering from blur, which black line partitions red, green, and blur color portions, and the like.